The present invention relates to a still image reader for obtaining still image data to be processed in a computer, wherein still image data of an optional scope are synthesized with data of partial images of an object obtained by an image input device.
Image input devices applied for obtaining still image data to be processed in a computer can be grouped into two categories according to types of image sensor applied therein, electronic still cameras and image scanners.
The electronic still camera, which can take an image with one shot without any mechanical structure for scanning the object, has superiority in its portability and handiness. On the other side, unable to take image of a wide scope with sufficient resolution, there is a problem that the object size should be limited in a narrow scope for extracting necessary information thereof, with the electronic still camera. Therefore, the electronic still camera, its resolution depending on a limited number of pixels of the two-dimensional area sensor applied therein, is regarded as inadequate for obtaining image data of precise pictures such as character documents or drawings.
On the contrary, in the image scanners such as flatbed type scanners or handy type scanners, there are problems of portability and limitation of scanning size for the flatbed type scanners having a certainly large scanning mechanism, or a problem of a narrow scanning width for the handy type scanners, even though the handy type scanners have little problem of the portability. Further, problem of complicated manipulation lies in both types of the image scanners, although they are superior in resolution for obtaining image data of character documents or drawings.
Still more, after taking image data, an editing operation, or trimming, is needed for clipping a desired part from the image data, either in the electronic still camera or the image scanner.
For resolving these problems of the conventional image input devices, there have been proposed several devices applying mosaic methods, that is methods wherein image data of a necessary scope are synthesized from partial image data obtained with necessary resolution from an object divided into several parts, making use of the two-dimensional area sensor not expensive by thus compensating its limitation of scope width.
The mosaic methods applied in these devices can be classified into four types according to methods for obtaining the partial image data, as follows:
first method: synthesizing partial image data obtained with a plurality of cameras each taking a photo of each of divided parts of an object; PA1 second method: synthesizing partial image data obtained by a plurality of CCD (Charge Coupled Device) units on which an image of an object is projected through a single optical system; PA1 third method: synthesizing partial image data obtained with a camera by displacing an object; and PA1 fourth method: synthesizing partial image data obtained from an object by displacing a camera. PA1 a position detector for detecting each position of the camera unit from where each of the plurality of partial images is taken; PA1 a frame for unitizing the position detector and the camera unit and enabling displacement of the camera unit parallel to the object; PA1 a partial image memory for storing data of the plurality of partial images; PA1 means for converting said each position of the camera unit into a corresponding position of the whole image to be synthesized where said each of the plurality of partial images is to be positioned; PA1 an image attribute table for storing attribute information including the corresponding position and a correction vector thereof for each of the plurality of partial images; PA1 means for calculating candidate vectors for each of the plurality of partial images referring to characteristic of the camera unit and the position detector, the candidate vectors indicating at least probable displacement from the corresponding position to coordinates where said each of the plulrality of partial images to be synthesized; PA1 means for selecting the correction vector to be stored in the image attribute table most appropriate among the candidate vectors by positioning trials of said each of the plurality of partial images referring to said each of the plurality of partial images, the attribute information and the candidate vectors for said each of the plurality of partial images; and PA1 means for synthesizing each of the plurality of partial images into the whole image according to the attribute information for said each of the plurality of partial images.
In the first method, of which an example is described in "Acquisition of Super High Definition Pictures by Processing Stereoscopic Images" by Aizawa et al., Technical Journal IE90-54, IEICE (the Institute of Electronics, Information and Communication Engineers), partial image data of each divided part of an object are taken by each of a plurality of cameras previously arranged for the object, and they are combined into image data of a desired scope. So, there is a necessity of distortion elimination for synthesizing from the partial image data obtained by cameras each having its own optical system, in addition to difficulty of arranging and preparing the camera positions appropriately.
In the second method, an optical picture focused by a single lens is received with a plurality of two-dimensional area sensors, for obtaining desired resolution by synthesizing partial image data taken therewith, such as described in "High Speed Still Image Reader using Optically Coupled Multi Area Sensors" by Uehira, the Journal of the IIEEJ (Institute of Image Electronics Engineers of Japan), Vol. 20, No. 3 (1991), pp. 203-208, or in "A Development of a Wide Scope Mosaic CCD Camera and a Prospect of Observational Cosmology" by Sekiguchi et al., BUTSURI, Vol. 47, No. 5 (1992), pp. 376-381, the Physical Society of Japan. Having a common optical system, camera operation such as focusing or exposure setting is not so difficult in the second method compared with ordinary cameras.
In these two methods, the resolution is improved making use of a plurality of two-dimensional area sensors, and so the resolution or the scope width is restricted by the limited pixel number of two-dimensional area sensors. The problem of editing operation is also left not improved, especially in the second method with two-dimensional area sensors generally arranged in a rectangle.
According to the third or the fourth methods, the partial image data of an object can be obtained by a single camera.
In the third method, of which an example is disclosed in a Japanese patent application by Kosaka, entitled "A Still Picture Input Device and a Method of Recording and Reproducing Still Pictures" and laid open as a Provisional Publication No. 96081/'91, the object is displaced for obtaining its partial image data by a fixed camera. So, a certainly large mechanism for the object displacement hinders portability of the whole system.
The fourth method, wherein the camera is displaced for obtaining the partial image data of a fixed object such as described in "A Hand-Scan Image Digitizer with an Ability for Realtime Assembling of Mosaic Pictures" by Okada et al., Technical Journal IE81-17, IE-ICE, or in a Japanese patent application by Mizoguchi et al., entitled "Image Input Device" and laid open as a Provisional Publication No. 259557/'94, enables the user to select desired parts of the object to be input by controlling the camera displacement, resolving the problem of trading off between the resolution and the scope width together with the posterior trimming.
However, even with the fourth method, there is left a problem, in these conventional mosaic methods, that an enormous calculation is needed for synthesizing the partial image data, which is to be performed referring to information extracted therefrom by analyzing patterns thereof, resulting in a high processing cost.
Furthermore, the mosaic method is susceptible of mis-synthesizing for an object with a monotonous texture having repeated patterns. For example, partial image data 401 and 402 illustrated in FIG. 15 may be synthesized into either image data 403 or image data 404 in the mosaic method and it can not be discriminated which are representing the correct object.
Still further, when the image input device, a CCD camera for example, is displaced manually, there may arise different distortions in different partial image data such as skews, magnifications or reductions, making correct synthesizing still more difficult.
These are problems of the mosaic method.